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Coronavirus Disease 2019

Testing

CORONAVIRUS TESTING BASICS

This 3 minute video in English and Spanish explains the basics of COVID-19 testing

PROTECTING OTHERS

  • People with COVID-19, even if they have no symptoms, can be very infectious and pass the infection to others.
  • No test is perfect, even if you test negative, it is still important to take steps to reduce the spread of COVID-19 and other infectious diseases.
  • If you have a fever with cough or shortness of breath or your doctor thinks that you have COVID-19, you need to isolate (separate yourself from others), and your close contacts need to quarantine. For more information visit lacounty.gov/covidisolation.
  • If you are a close contact to a person confirmed or suspected to have COVID-19, you need to quarantine (stay home; separate yourself from others to “wait and see” if you develop the illness) even if you get a negative test result. For more information visit http://ph.lacounty.gov/covidquarantine.
  • The best way to reduce the risk of COVID-19 is to practice everyday prevention, including keeping your distance from others, wearing a cloth face covering correctly over both your nose and mouth, and washing your hands often. Choose wisely and avoid the 3 C’s (confined spaces, crowding, and close contact).

TYPES OF COVID-19 TEST

DIAGNOSTIC (VIRAL) TESTS

Shows current infection

ANTIBODY TEST

Shows past infection

Also known as

Molecular Test

  • Diagnostic test
  • Nucleic acid amplification test (NAAT)
  • Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR or PCR)

Antigen Test

  • Rapid diagnostic test

Antibody Test

  • Serology
  • Serological test
  • Blood test

When the test is recommended

  • For people with symptoms of COVID-19
  • For people who were close contacts to COVID-19
  • For people without symptoms living/working in a high risk setting who are identified as part of an outbreak detection and response
  • For people with symptoms of COVID-19 (recommended soon after their symptoms started).
  • Recommended only for certain situations. See “uses of serology
  • NOT for diagnosing a current infection
  • NOT to show a person does not have COVID-19

How the test works

Detects genetic material from the COVID-19 virus

Detects proteins on the surface of the COVID-19 virus

Detects antibodies, made by the body’s immune system in response to a COVID-19 infection. It takes 1-3 weeks after a person is infected for antibodies to show on the test.

Type of sample

Nose or throat swab or saliva

Nose or throat swab

Blood (from a finger stick or blood draw)

How long it takes to get results

Typically, 2-6 days but some locations offer same day or even one- hour results

One hour or less

Same day to 3 days

What the test does

Checks for active coronavirus infection

Checks for active coronavirus infection

Checks for past coronavirus infection

What a positive result means*

A positive result means you have COVID-19. The test detected the COVID-19 virus. 

NOTE: If you re-tested within 3 months of having recovered from COVID-19, your test may still be positive. This is because the test can also detect material from the dead virus. Talk to your doctor.

A positive result means you have COVID-19. The test detected the COVID-19 virus.

A positive result means that you have been infected by COVID-19 in the past. The test detected antibodies to the COVID-19 virus.

What a negative result means*

A negative result means the test did not detect the virus at the time the test was taken.

A negative result can also happen if the test was taken too early or the test missed your infection.

Note: If you are a close contact to a person with COVID-19 you must remain under quarantine for the entire 14-day period because you may still develop the disease and it was too early for your test to be positive (if you are infected).

A negative result means the test did not detect the virus at the time the test was taken.  It is recommended that you now get a molecular test because antigen tests often miss infections.

Note: If you are a close contact to a person with COVID-19 you must remain under quarantine for the entire 14-day period because you may still develop the disease and it was too early for your test to be positive (if you are infected).

A negative result means the test did not detect antibodies to the COVID-19 virus and you may have never had COVID-19 (see antibody section below).

*No test for COVID-19 is perfect. Any test may produce:

  • False negative results
    • This means that the test result should be positive because you DO have COVID-19, but instead it comes back negative.
    • This may happen, for example, if the sample was not collected properly, the test was taken too soon, or the test didn’t perform well.
  • False positive results
    • This means that the test result should be negative because you DO NOT have COVID-19 but instead it comes back positive.
    • This may happen, for example, if the person tested is very unlikely to be infected and the test didn’t perform well.

TESTING FOR CURRENT COVID-19 INFECTION: Diagnostic (Viral) Tests - Molecular and Antigen Tests

Which Test is Recommended to Look for Current Infection

  • Molecular tests are recommended to check for current infection because they are better than antigen tests at detecting the virus that causes COVID-19.
  • Antigen tests are faster than most molecular tests, but they do not work as well and miss many more infections. Because of this, if you have a negative antigen test result you should be tested again with a molecular test, especially if you have symptoms of COVID-19. 
  • Serology tests are not recommended to look for current infection.
  • Ask your provider which type of test they are using.

When Testing is Recommended

Testing is highly recommended for:

  • People who have symptoms: If you have symptoms of COVID-19, contact a healthcare provider and discuss if you should be tested.
  • People without symptoms who:
    • Have been a “close contact” to someone with confirmed or suspected COVID-19 (a case) within the last 14 days. Even if your test is negative, you will still need to stay in and complete your quarantine.
    • Are part of an outbreak response or contact investigation in high risk settings, such as nursing homes, congregate living facilities, correctional facilities, or persons experiencing homelessness.

Testing is not recommended for people who had a positive viral COVID-19 test in the last three months if they have already passed their isolation period and do not currently have symptoms of COVID-19.

How To Get a Test

  • Call your healthcare provider. If you need help finding a health care provider, call 2-1-1 or visit the 211LA
  • People who live in LA County, regardless of immigration status, can apply for an appointment for a drive through or walk up test by visiting lacounty.gov/testing or by calling 2-1-1.
  • You can also get a test at some pharmacies. Check with your local pharmacy.
  • Beware of COVID-19 testing scams – visit our COVID-19 scams and fraud page for more information.

Paying For a Test to Diagnose COVID-19

  • Health insurers are required (by federal law) to cover the entire cost of testing for the virus whether you have symptoms or not. A doctor will need to order the test.
  • Testing through the County of Los Angeles and the City of Los Angeles mobile testing sites is free for all LA County residents who meet the criteria for testing, regardless of their immigration status.

Questions To Ask Before You Get A Test

  • What type of test you are being offered (see table).
  • How long it will take to get your results
  • How you will find out the results.
  • What precautions you should take while you wait for your results and what you should do if your result is positive or is negative

After the test, make sure that you understand what your result means.

TESTING FOR PAST COVID-19 INFECTION: ANTIBODY TESTS (Serology)

Antibody tests (also known as serology tests) are blood tests that look for antibodies against a virus. They do not look for the virus itself. Antibodies are proteins that are made by the immune system to help fight infection. It takes about one to three weeks after the start of COVID-19 symptoms for the body to make enough antibodies to be found by a test. Some people may take even longer and some people who were infected with COVID-19 may never develop antibodies.

We do not know yet if having antibodies to the virus can protect someone from getting infected again, and if it does, how long that protection (immunity) might last. Until more is known, even if you had a positive antibody test, you should continue to practice everyday prevention to protect yourself and others, including keeping your physical distance from others, correctly wearing a cloth face covering, and washing your hands often. Continue to choose wisely and avoid the 3 C’s (confined spaces, crowding, and close contact).

Antibody test results should not be used to determine if someone can return to work or to decide who can spend time together.

To learn more about using antibody tests to look for past infection, visit the CDC webpage.

Uses of antibody tests

To guide the management of someone with complicated symptoms

There are situations where a serology test may be helpful (in addition to a viral test) to diagnose COVID-19, such as:

  • If someone develops complications late in an illness that may be associated with COVID-19, such as multisystem inflammatory syndrome in children (MIS-C).
  • If someone had symptoms of COVID-19 for several weeks and the viral tests were negative.

To find blood donors for COVID-19 treatment

Serology tests can be used to find people who have had COVID-19 infection in the past. They may be able to donate blood that can be used to help treat patients with severe COVID-19 disease.

For science and public health

Scientists and Public Health organizations are using antibody tests to learn more about how the immune system responds to the COVID-19 virus over time. Antibody tests can tell how many people in a community may have been infected in the past and how far the pandemic has progressed. They can also be used to help understand why some people get infected but never show any symptoms (asymptomatic infection).

MORE INFORMATION

  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: Explains the different types of tests, and how they are performed and approved. PDF webpage
  • White House/DHHS Guidance on Interpreting COVID-19 test results: A one-page table on how to interpret test results (including when a combination of tests is done) and determining what actions to take according to the results.
  • LAC DPH COVID-19 Guidance Based on [molecular] Test Results: English
  • LAC DPH COVID-19 Serology [Antibody] Test FAQs: English


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  • Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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